The conference brought together representatives from the three main monotheistic faiths, Islam, Christianity and Judaism, as well as Buddhism.

A photo of King Abdullah and Benedict XVI taken during Abdullah's historic visit to the Vatican last November has been posted with the video to publicise it on Islamist websites.

A caption beneath the photo repeats part of al-Libi's video message. It reads: "He (Abdullah) has made religion a joke and has done so in public with Jews, Christians and Muslims.

"He has thrown those fighting for Islamism into jail...and has fraternised with those who have offended the Prophet, notably the adulator of the Cross, the Vatican's Pope."

Al-Libi also attacks Muslim religious leaders, claiming they have colluded in inter-religious dialogue by sitting alongside exponents of other faiths

"The Prophet ordered us to drive unbelievers from the Arabian Peninsula. Today, the Saudi royal family is destroying our Islamic tenets by showing Muslims it is possible to spread Christian principles."

"By sitting side by side in public, they are taking part in the Crusader campaign. They are helping them, giving information to their secret services, all in order to spread their culture and religion."

Al-Libi concludes the message with a call to kill King Abdullah for having betrayed Islam.

The Libyan-born militant is believed to have fought alongside al-Qaeda leader Osama Bin Laden in Afghanistan.